1. Field of the Invention
The present invention relates to a hydraulic/pneumatic cylinder, and, more particularly, to a hydraulic/pneumatic reinforced polymeric composite cylinder with a removable end plug.
2. Description of the Related Art
Hydraulic and pneumatic cylinders are utilized for converting pressurized fluid into mechanical movement in a controlled manner. Hydraulics allow for the amplification of mechanical force by translating a pressure applied against a surface to force a piston to move inside of the cylinder, the piston being connected to a shaft that extends beyond the cylinder to thereby move a connected assembly. Air cylinders are often used in environments where hydraulic fluids would be undesirable, such as in food processing facilities.
In a typical hydraulic/pneumatic cylinder, one end of the cylinder is enclosed with a plug and an opposite end is enclosed with a plug having a hole therein for accommodating a shaft that moves therethrough. Periodically cylinders are rebuilt by disassembling the cylinder and replacing worn parts.
The most common and simplest form of attaching ends to a cylinder is by way of tie rods that extend from one end of a cylinder to the other. In this configuration a composite cylinder tube can normally be interchanged with an existing metallic cylinder made of aluminum, stainless steel or carbon steel. However, in cases where tie rod designs are not desirable or permissible it becomes difficult to attach removable ends.
Additional ways of connecting removable ends to metallic cylinders include, machining threads on to the end caps and the cylinder bores, thereby providing a way to remove and install an end cap by screwing the parts together. Machining an annular groove in the bore of the cylinder and using a retaining ring to hold the end cap in place. Also, the end cap can be held in place by way of radially positioned screws located around the circumference of the cylinder that thread into the end cap.
Problems associated with these methods relative to reinforced polymeric composite cylinders include: Cutting threads into a filament wound composite severs the reinforcing members of the composite thereby substantially reducing the shear strength at the thread location. For example, the reinforcing members such as fiberglass can contribute an order of magnitude over the strength of the matrix in a composite. If these continuous members are cut, the strength of the composite is greatly reduced. Upon repeated assembly the threads tend to break down easily due to low shear strength of the threads. The conventional design for the use of retaining rings in a composite is not desirable due to the eroding of the groove in the composite cylinder tube by the metallic retaining ring under cycling conditions. It has been found upon repeated cycling the retainer ring will erode the groove in such a manner that a ramp is formed allowing the ring to work its way out of the groove and thereby releasing the end caps. Bolting or pinning the end attachment by radial orientated fasteners around the circumference of the tube is not desirable due to the cutting of reinforcement through the entire thickness of the laminate at the holes, stress concentrations at the hole locations and potential micro-cracking in the laminate at the hole locations which could result in crack propagation under stress cycling conditions.
What is needed in the art is a pneumatic/hydraulic cylinder that allows simple assembly techniques and is easy to disassemble for maintenance purposes.